In the general field of earth structures such as open pit slopes, tailings dams, foundation work, tunnel excavations, underground mines, and the like, it is well known that stresses within the earth media surrounding the structure or within the structure may exceed the structure's strength and cause a failure. If there is no warning of such a failure, the consequences may be catastrophic, especially in terms of the loss of lives of workers caught in a collapsing structure.
It is known, at least theoretically, that such failures do not occur without tell-tale prior warning signals. That is, as the stresses within an earth structure approach the critical maximum strength of the earth materials, the structure beings to deform or creep long before failure. Although the velocity of such creep deformation is quite small compared with the movement which occurs during a failure, it can be measured. Measurement of the magnitude and direction of the microscopic creep velocity discloses the nature and cause of the potential failure. With quantitative knowledge of the micro-creep behavior, the potential failure may be predicted, and consequently, necessary measures may be taken to avert such a failure. The technological realization of this theoretical knowledge has been less than optimum to date, as witnessed by the many mine cave-ins, slope failures, and the like, throughout the world. This is due in part to the fact that the micro-creep velocity prior to failure is quite small. Existing state-of-the-art devices for measuring creep have a limited sensitivity, and require a rather long time period to develop significant data regarding the nature and magnitude of the ground creep velocity. In situations such as advanced tunnel excavations or underground mining, or open pit mining, the prior art creep measuring devices cannot be set up for a sufficient time to gain significant data, as they commonly interfere with construction or mining activity. Economic considerations dictate that these devices will be set aside in favor of maintaining mine output or excavation progress.